Index: /trunk/ppImage/src/ppImageDetrendReadout.c
===================================================================
--- /trunk/ppImage/src/ppImageDetrendReadout.c	(revision 10414)
+++ /trunk/ppImage/src/ppImageDetrendReadout.c	(revision 10415)
@@ -73,4 +73,10 @@
     float norm = psMetadataLookupF32(&mdok, config->arguments, "NORMALISATION");
     if (mdok && isfinite(norm) && norm != 1.0) {
+        pmHDU *hdu = pmHDUFromReadout(input); // HDU of interest
+        psString comment = NULL;        // Comment to add
+        psStringAppend(&comment, "Normalisation: %f", norm);
+        psMetadataAddStr(hdu->header, PS_LIST_TAIL, "HISTORY", PS_META_DUPLICATE_OK, comment, "");
+        psFree(comment);
+
         psBinaryOp(input->image, input->image, "*", psScalarAlloc(norm, PS_TYPE_F32));
     }